As radio-frequency (RF) and optical electromagnetic signals do not propagate well under the ocean surface or through land, alternative communication methods are to be used for these environments. There are multiple alternative options, each having advantages and disadvantages. Therefore, different approaches may be taken depending on applications. For example, some applications may use a tether to communicate by wire or optical fiber, which can impose maneuvering limits or hazards involving physical contact with vehicles or structures. As another example, acoustic communications are often used, but are affected by multipath and shallow-water resonances, with the consequence that robust acoustic communications have a very low bit rate. Yet, another candidate can be near-field magnetic communications, which works with low-frequency signals, to be measurable at longer ranges thereby limiting bit rate, and signals which have a rapid drop off in signal strength at longer ranges.
Traditional modulation schemes used in magnetic communications have a low bit-rate for a given range. If the bit rate could be increased substantially, a variety of applications could benefit from these traditional modulation schemes. For example, one motivating application is the use of unmanned underwater vehicles (UUV) for sensing tasks underwater, such as oil rig inspection or sea-floor pipeline, or well-head inspection. Currently, most data is stored until the vehicle surfaces, meaning that operators have little awareness of how the mission is proceeding and little ability to influence its course, such as re-inspecting an area of interest, or recognizing that the UUV has incorrectly identified a rock as a well head. Another motivating example is a stationary sensor on the ocean floor, which needs to send data to the surface or to a passing underwater vehicle when the opportunity arises.